Novel synthesis of 1,2,4-triazolo[4,3-a]pyrimidin-5-one derivatives

Article abstract of DOI:10.1016/S0040-4020(01)01026-2

1,2-Dihydro-2-thioxopyrimidin-4(3H)ones 6 react with C-ethoxycarbonyl-N-arylhydrazonoyl chlorides 1 to give 1,2,4-triazolo[4,3-a]pyrimidines 11 in good yield. The latter products 11 react with benzenediazonium chloride, nitrous acid, acetyl chloride and chloroacetyl chloride to give the corresponding substitution products 16-18. The structures of the newly synthesized compounds are established on the basis of chemical and spectroscopic evidence.

Full text of DOI:10.1016/S0040-4020(01)01026-2

TETRAHEDRON
Pergamon
Tetrahedron 57&2001) 10133±10138
Novel synthesis of 1,2,4-triazolo[4,3-a]pyrimidin-5-one derivatives
Hamdi M. Hassaneen,p Hyam A. Abdelhadi and Tayseer A. Abdallah
Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt
Received 29 December 2000; revised 3 September 2001; accepted 27September 2001
AbstractÐ1,2-Dihydro-2-thioxopyrimidin-4&3H)ones 6 react with C-ethoxycarbonyl-N-arylhydrazonoyl chlorides 1 to give 1,2,4-tria-
zolo[4,3-a]pyrimidines 11 in good yield. The latter products 11 react with benzenediazonium chloride, nitrous acid, acetyl chloride and
chloroacetyl chloride to give the corresponding substitution products 16±18. The structures of the newly synthesized compounds are
established on the basis of chemical and spectroscopic evidence. q 2001 Published by Elsevier Science Ltd.
1. Introduction
previous results with related compounds2,3 these products
did not contain sulfur. On the basis of this ®nding the
structures 7±10 &Scheme 1) were discarded for the products
isolated. The spectral and elemental analytical data are
compatible, however, with one of the two isomeric
structures 11 or 12 &Scheme 1).
Previously, we reported that hydrazonoyl halides 1 react
with thiourea and with heterocyclic compounds containing
a thiourea moiety to give the corresponding thiadiazoline 3
and triazoloazines 4 or 5, respectively.1±3 The angular struc-
ture 4 was tentatively assumed for these products on the
basis of N1 is more basic due to the effect of carbonyl
group,4,5 however on solid structure proof has been given.
The proposed mechanism leading to the formation of the
latter products 11 or 12 suggested that the studied reactions
involve an initial formation of thiohydrazonoate esters 7 or
amidrazones of type 13. The latter amidrazones 13 was
excluded on the basis of &1) although amidrazones of type
13 are known to be stable,1,6,7 all attempts to separate them
from the reaction mixture failed in all cases; &2) reaction of
2-thiouracile derivatives with various halogen compounds
yielded in all cases S-substituted products.8±11 The thio-
hydrazonoate esters 7 undergo an S!N migration via the
spiro intermediates 8, to give the thiohydrazides 9. The spiro
intermediates 8 may also be formed via 1,3-dipolar cyclo-
addition of nitrilimines 2, generated in situ from reaction of
hydrazonoyl chlorides 1 with triethylamine, to the thione
group CvS of 6. The latter intermediates 9 undergo cycli-
zation followed by elimination of hydrogen sul®de to give
the ®nal products 11 or 12 &Scheme 1).
In the present investigation, we report on the reaction of
1,2-dihydro-2-thioxopyrimidin-4&3H)one derivatives 6 with
hydrazonoyl chlorides 1 and determine the structure of
the products in addition to their reactivity towards some
electrophiles. The newly synthesized compounds appear to
be promising for further chemical transformations as well as
biological activity evaluations.
All these products gave a singlet signal at d 5.5 in their 1H
NMR spectra assignable to pyrimidine CH and showed
three stretching frequencies near 3281, 1750 and
1687cm 21 assignable to NH, ester CO and amide CO
groups, respectively. These data cannot determine the
exact structure for the resulting products and conclusive
evidence for the structure 11 was obtained by X-ray crystal-
lographic analysis of a crystal of the product 16a resulting
from reaction of 11a with benzenediazonium chloride.
2. Results and discussion
The reaction of 6 with hydrazonoyl chlorides 1 was carried
out in chloroform in the presence of triethylamine under
re¯ux. After work up of the reaction mixture, only a single
product was isolated, in each case. As expected from all our
Keywords: 1,2-dihydro-2-thioxopyrimidin-6-phenylamino-4&3H)ones;
C-ethoxycarbonyl-N-arylhydrazonoyl chlorides; 1,2,4-triazolo[4,3-a]-
pyrimidine-5-ones.
Corresponding author. Tel.: 120-5676571; fax: 120-25726406;
e-mail: hamdi251@hotmail.com
Compounds 11a and 11d are readily coupled with equi-
molar amount of benzenediazonium chloride to yield exclu-
sively the corresponding 6-phenyl-azo derivatives 16a and
p
0040±4020/01/$ - see front matter q 2001 Published by Elsevier Science Ltd.
PII: S0040-4020&01)01026-2

10134
H. M. Hassaneen et al. / Tetrahedron 57 '2001) 10133±10138
Scheme 1.
16b, respectively &Scheme 2). The structures of the latter
products were established basis on elemental and spectral
analyses &IR, 1H NMR, MS). For example, 1H NMR
spectrum of 16a revealed the absence of singlet signal at
d 5.5 &pyrimidine CH). Also, the structures of 16a and 16b
were con®rmed by their alternative synthesis from reaction
of 5-phenylazo-1,2-dihydro-2-thioxopyrimidin-4&3H)ones
14a and 14b with compound 1a, respectively &Scheme 2).
Furthermore, the structure of the product 16a was con®rmed
by X-ray crystallography &Fig. 1).
a two signals at d 2.2 and 2.8 corresponding to acetyl groups
in compounds 18a and 18b, respectively, and a singlet
signal at d 5.1 assignable to the chloroacetyl group in
compound 18c.
2.1. X-Ray crystallographic study of compound 16a
The molecular structure and numbering scheme is depicted
in Fig. 1. The crystals were quite small and of low quality
with some re¯ection pro®les showing shoulders, but the
overall structure is clearly de®ned. The amine group
forms an intramolecular hydrogen bond with the outer
N-atom of the NvN group. The two fused rings are planar.
Both the phenyl substituent of N&6) and the ±NvN±Ph
group are virtually coplanar with the fused rings, although
the phenyl substituent at N&6) is titled slightly out of the
plane due to the slight pyramidalization at N&6). The other
substituents do not lie close to the fused ring plane.
Nitrozation of compounds 11 with sodium nitrite in acetic
acid yielded the corresponding 6-nitrosotriazolo[4,3-a]pyri-
midine derivatives 17 in excellent yield. These compounds
are also prepared by reaction of 5-nitroso-1,2-dihydro-2-
thioxopyrimidin-4&3H)one 15 with hydrazonoyl chlorides
1 &Scheme 2). The structures of the products 17 were also
con®rmed by elemental and spectral data.
Acylation of compounds 11 with acetyl chloride and chloro-
acetyl chloride furnished the corresponding substitution
product 18a±18c. Elemental analysis and spectroscopic
data con®rmed the structure 18a±18c. For example, the
1H NMR spectra of the latter products revealed the absence
of singlet signal at d 5.5 of compound 11, instead it showed
3. Experimental
Melting points were taken on a Gallenkamp apparatus and
are uncorrected. Infrared spectra &KBr) were determined on
a Pye Unicam SP-3000 infrared spectrophotometer. 1H

H. M. Hassaneen et al. / Tetrahedron 57 '2001) 10133±10138
10135
Scheme 2.
NMR spectra were determined on a Varian Gemini 200
spectrometer &200 MHz) in CDCl3 with TMS as an internal
standard. Mass spectra were recorded on a GCMS-QP
1000EX Shimadzu, Japan. Elemental analyses were carried
out at the microanalytical center, University of Cairo,
Giza, Egypt. The C-ethoxycarbonylhydrazonoyl chlorides
1a±1d12 and 6,13 1413 and 1513 were prepared as previously
described.
4.55 &q, Jˆ7Hz, 2H), 5.49 &s, 1H, pyrimidine CH), 7.0 &s,
1H, NH), 7.13±8.21 &m, 10H); MS, m/z: 375, 303, 275, 220,
187, 144, 93, 77. Anal. calcd for C20H17N5O3: C, 64.0; H,
4.5; N, 18.7. Found: C, 64.1; H, 4.7; N, 18.4%.
3.1.2. Ethyl /1-/p-tolyl)7-phenylamino-5-oxo-1,2,4-tria-
zolo[4,3-a]pyrimidin-3-yl)carboxylate 11b. The com-
pound was obtained in 80% yield, yellow crystal mp
2068C &acetic acid); IR &KBr) n 3281 &NH), 1750 &CvO),
1
1689 &CvO) cm21; H NMR &CDCl3) d 1.49 &t, Jˆ7Hz,
3.1. Synthesis of 1,2,4-triazolo[4,3-a]pyrimidin-5-ones
11a±11d: general method
3H); 2.42 &s, 3H); 4.60 &q, Jˆ7Hz, 2H); 5.49 &s, 1H, pyri-
midine CH), 6.93 &s, 1H, NH), 7.26±8.0 &m, 9H); MS, m/z:
389, 227, 207, 144, 105, 60. Anal. calcd for C21H19N5O3: C,
64.8; H, 4.9; N, 18.0. Found: C, 64.6; H, 4.7; N, 17.8%.
To a stirred solution of the appropriate hydrazonoyl
chlorides 1 &5 mmol) and 2-thioxopyrimidin-4&3H)one 6
&5 mmol) in chloroform &40 ml) was added triethylamine
&0.7ml, 5 mmol) at room temperature. The reaction mixture
was re¯uxed until the hydrazonoyl halide disappeared
&4±6 h) as indicated by TLC analysis. The solvent
was evaporated under reduced pressure and the residue
was treated with methanol &10 ml). The solid formed was
collected and crystallized from a suitable solvent to give
the corresponding 1,2,4-triazolo[4,3-a]pyrimidin-5-ones
11a±11d.
3.1.3. Ethyl /1-/p-chlorophenyl)7-phenylamino-5-oxo-
1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate 11c. The
compound was obtained in 78% yield, white crystal mp
2318C &acetic acid); IR &KBr) n 3287&NH), 1741 &C vO),
1
1692 &CvO) cm21; H NMR &CDCl3) d 1.42 &t, Jˆ7Hz,
3H), 4.52 &q, Jˆ7Hz, 2H), 5.45 &s, 1H, pyrimidine CH),
6.97&s, 1H, NH), 7.26±8.23 &m, 9H); MS, m/z: 409, 353,
277, 229, 183, 133, 77. Anal. calcd for C20H16ClN5O3: C,
58.7; H, 3.9; N, 17.1. Found: C, 58.8; H, 4.0; N, 17.0%.
3.1.1. Ethyl /1-phenyl-7-phenylamino-5-oxo-1,2,4-tria-
zolo[4,3-a]pyrimidin-3-yl)carboxylate 11a. The com-
pound was obtained in 85% yield, pale yellow crystal mp
1738C &ethanol); IR &KBr) n 3272 &NH), 1746 &CvO), 1687
3.1.4. Ethyl /1-phenyl-7-amino-5-oxo-1,2,4-triazolo[4,3-a]-
pyrimidin-3-yl)carboxylate 11d. The compound was
obtained in 77% yield; pale yellow crystal mp 2248C &acetic
acid); IR &KBr) n 3471, 3284 &NH2), 1741 &CvO), 1668
1
&CvO) cm21; H NMR &CDCl3) d 1.42 &t, Jˆ7Hz, 3H),

10136
H. M. Hassaneen et al. / Tetrahedron 57 '2001) 10133±10138
Figure 1. Diagram of compound 16a with crystallographic numbering system.
1
1
&CvO) cm21; H NMR &CDCl3) d 1.45 &t, Jˆ7Hz, 3H),
&CvO) cm21; H NMR &CDCl3) d 1.50 &t, Jˆ7Hz, 3H),
4.57&q, Jˆ7Hz, 2H), 4.92 &s, 2H, NH 2), 5.16 &s, 1H, pyri-
midine CH), 7.33±8.09 &m, 5H); MS, m/z: 299, 271, 226,
197, 173, 159, 105, 77, 68, 51. Anal. calcd for C14H13N5O3:
C, 56.2; H, 4.4; N, 23.4. Found: C, 56.0; H, 4.5; N, 23.3%.
4.64 &q, Jˆ7Hz, 2H), 7.19±8.14 &m, 15H), 13.90 &s, 1H,
NH); MS, m/z 479, 450, 402, 328, 275, 220, 129, 91, 77.
Anal. calcd for C26H21N7O3: C, 65.1; H, 4.4; N, 20.5. Found:
C, 65.3; H, 4.2; N, 20.2%.
3.2.2. Ethyl /1-phenyl-6-phenylazo-7-amino-5-oxo-1,2,4-
triazolo[4,3,-a]pyrimidin-3-yl)carboxylate 16b. The com-
pound was obtained in 72% yield; orange crystal mp 2308C;
IR &KBr) n 3446, 3280 &NH2), 1747 &CvO), 1712 &CvO)
cm21; 1H NMR &CDCl3) d 1.52 &t, Jˆ7Hz, 3H), 4.66 &q, Jˆ
7Hz, 2H), 6.06 &s, 2H, NH 2), 7.32±8.10 &m, 10H); MS, m/z
403, 375, 326, 270, 232, 131, 91, 77, 51; Anal. calcd for
C20H17N7O3: C, 59.6; H, 4.2; N, 24.3. Found: C, 59.9; H,
4.1; N, 24.4%.
3.2. Synthesis of ethyl /1-phenyl-6-phenylazo-5-oxo-1,2,4-
triazolo[4,3-a]pyrimidin-3-yl)carboxylate derivatives
16a and 16b
MethodA . To a solution of 11a,d &5 mmol) in ethanol
&100 ml), sodium hydroxide &0.2 g, 5 mmol) was added.
The mixture was then treated gradually with stirring at
room temperature with a solution of benzenediazonium
chloride &prepared from aniline &0.5 ml, 5 mmol) and the
appropriate quantities of hydrochloric acid and sodium
nitrite). The product was separated on standing, collected
by ®ltration and crystallized from diemthylformamide to
give 16a and 16b.
3.3. Synthesis of ethyl /1-aryl-6-nitroso-7-phenylamino-
5-oxo-1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate
17a±17c
MethodB . Compounds 16a and 16b were prepared by the
same method described for the synthesis of 11 using 5-
phenylazo-2-thioxopyrimidin-4&3H)-one derivatives 14a
and 14b in place of 6. The products were identical in all
respects &mp, mmp, IR) to those resulting from method A.
MethodA . To a solution of 11 &5 mmol) in acetic acid
&10 ml), a concentrated solution of sodium nitrite &2 g in
5 ml water) was added with stirring. The solid that formed
was collected and crystallized from ethanol to give
17a±17c.
3.2.1. Ethyl /1-phenyl-6-phenylazo-7-phenylamino-5-
oxo-1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate 16a.
The compound was obtained in 70% yield; orange crystal
mp 2538C; IR &KBr) n 3210 &NH), 1753 &CvO), 1701
MethodB . Compounds 17 were prepared by the same
method described for the synthesis of 11 using 6-phenyl-
amino-5-nitroso-1,2-dihydro-2-thioxopyrimidine-4&3H)one

H. M. Hassaneen et al. / Tetrahedron 57 '2001) 10133±10138
10137
15a±15c in place of 6. The products were identical in all
respects to those obtained by method A.
oxo-1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate 18c.
The compound was obtained in 77% yield; white crystal
mp 1748C &ethanol); IR &KBr) n 3250 &NH), 1735
&CvO), 1700 &CvO), 1667&C vO) cm21 1H NMR
;
3.3.1. Ethyl /1-phenyl-6-nitroso-7-phenylamino-5-oxo-
1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate 17a. The
compound was obtained in 70% yield, pale yellow crystal
mp 1928C; IR &KBr) n 3220 &NH), 1750 &CvO), 1700
&CDCl3) d 1.50 &t, Jˆ7Hz, 3H), 4.62 &q, Jˆ7Hz, 2H),
5.09 &s, 2H), 7.35±8.06 &m, 10H), 12.77 &s, 1H, NH); MS,
m/z: 451, 416, 402, 330, 288, 213, 144, 77. Anal. calcd for
C22H18ClN5O4: C, 58.5; H, 4.0; N, 15.5. Found: C, 58.6; H,
4.1; N, 15.6%.
1
&CvO) cm21; H NMR &CDCl3) d 1.43 &t, Jˆ7Hz, 3H),
4.45 &q, Jˆ7 Hz, 2H), 7.23±7.92 &m, 10H), 11.78 &s, 1H,
NH). Anal. calcd for C20H16N6O4: C, 59.4; H, 4.0; N, 20.8.
Found: C, 59.5; H, 4.1; N, 20.7%.
3.5. X-Ray analysis
3.3.2. Ethyl /1-/p-tolyl)-6-nitroso-7-phenylamino-5-oxo-
1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxylate 17b. The
compound was obtained in 69% yield; white crystal mp
1858C; IR &KBr) n 3218 &NH), 1748 &CvO), 1700
The structure was solved by direct methods using SIR927,
which revealed &CCDC Ref. no. 155856) the positions of all
non-hydrogen atoms. The non-hydrogen atoms were re®ned
anisotropically. All of the H-atoms were ®xed in geo-
1
&CvO) cm21; H NMR &CDCl3) d 1.44 &t, Jˆ7Hz, 3H),
Ê
metrically calculated positions [d&C±H)ˆ0.95 A] and each
2.42 &s, 3H), 4.47&1, Jˆ7 Hz, 2H), 7.26±7.80 &m, 9H),
11.87&s, 1H, NH). Anal. calcd for C 21H18N6O4: C, 60.3;
H, 4.3; N, 20.1. Found: C, 60.1; H, 4.1; N, 20.0%.
was assigned a ®xed isotropic displacement parameter with
a value equal to 1.2Ueq of its parent C-atom. Re®nement of
the structure was carried out on F using full-matrix least-
squares procedures, which minimized the function
ꢀuFou 2 uFcu†:14 The weighting scheme was based on count-
P
3.3.3. Ethyl /1-/p-chlorophenyl)-6-nitroso-7-phenyl-
amino-5-oxo-1,2,4-triazolo[4,3-a]pyrimidin-3-yl)carboxyl-
ate 17c. The compound was obtained in 65% yield; pale
yellow crystal mp 1758C; IR &KBr) n 3200 &NH), 1748
ing statistics and included a factor to downweight the
P
14
intense re¯ections. Plots of ꢀuFou 2 uFcu† verse uFou;
re¯ection order in data collection, sin u=l; and various
classes of indices showed no unusual trends. A correction
for secondary extinction was applied.
1
&CvO), 1701 &CvO) cm21; H NMR &CDCl3) d 1.43 &t,
Jˆ7Hz, 3H), 4.45 &q, Jˆ7Hz, 2H), 7.23±8.97 &m, 9H),
11.87&s, 1H, NH). Anal. calcd for C 20H15ClH6O4: C, 54.7;
H, 3.4; N, 19.2. Found: C, 55.0; H, 3.5; N, 19.1%.
Neutral atom scattering factors for non-hydrogen atoms
were taken from Maslen, Fox and O'Keefe,15 and the
scattering factors for H-atoms were taken from Stewart et
al.16 Anomalous dispersion effects were included in Fc;17 the
values for f0 and f00 were those of Creagh and McAuley.15
The values of the mass attenuation coef®cients are those of
Creagh and Hubbell.15 All calculations were performed
using the teXsan crystallographic software package.18
3.4. Synthesis of ethyl /1-phenyl-6,7-disubstituted-5-oxo-
1,2,4-triazolo-[4,3-a]pyrimidin-3-yl)carboxylate 18a±18c:
general procedure
Compounds 11a,d &5 mmol) was re¯uxed in acetyl chloride
&10 ml) or chloroacetyl chloride &10 ml) for 3 h. The
reaction mixture was cooled and the solid formed was
collected and crystallized from suitable solvent to give
products 18a±18c.
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pound was obtained in 75% yield; white crystal mp 2458C
&DMF±ethanol); IR &KBr) n 3340, 3132 &NH2), 1720
&CvO), 1712 &CvO), 1689 &CvO) cm21 1H NMR
;
&CDCl3) d 1.53 &t, Jˆ7Hz, 3H), 2.21 &s, 3H), 4.60 &q, Jˆ
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4.4; N, 16.7%.
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